In most applications, air cylinders are used to achieve the sliding, turning or upward and downward motions of some machine component or external load to be processed. In certain lumber making operations cylinder stroking at high speed and frequency is called for where the inertial resistance of the displaced load may be high in relation to the cylinder size.
One concrete example is the case of a lumber trimming saw assembly which, in the modern context of production, must be lowered and lifted by a pneumatic cylinder a number of times per second, through a vertical distance of several inches. Up to very few years ago, the maximum cycling frequency of such an assembly was of the order of 90 cuts per minute, whereas present day applications reach up to twice that number. It can be estimated that, in a high speed lumber trimming application, an industrial class pneumatic cylinder equipped with standard built-in cushions would not last more than a few work shifts before requiring parts replacements. The production losses and the extra maintenance caused by cylinder break-down in the lumber trimming phase is compounded by the number of saw units involved (up to seventeen) in a mill producing 6' to 16' lumber with the option of selective trimming in odd or even foot lengths. Since every sawmill must have a trimming operation of sufficient capacity and versatility for the total production and all market requirements, it follows that in order to meet operating conditions, an efficient and reliable means of cushioning the saw cylinder at the end of each stroke becomes a matter of necessity.
Other cylinder cushioning options, such as resilient inserts to prevent metal-to-metal contact of the piston with the cylinder heads, have not proven satisfactory in high cycling operations as the repetitive hammering within the cylinder causes a rapid break-down of the inserts which finally disintegrate and foul-up the valve circuit.
Another cushioning method consists of increasing the compression volume within the cylinder itself, by extending the barrel length beyond the actual piston travel requirements. This can be effective in some applications but not whenever exact positioning of the load at stroke end is necessary, such as in the field of application mentioned above.